Cross-guide couplers are known in the art for handling RF waves. Typically, cross-guide couplers are used for measuring and monitoring RF signals propagating through a waveguide arrangement and/or for combining multiple RF signals. For example, a common use for waveguide couplers is to sample a signal within a waveguide network in order to monitor the operation of a circuit, which may for example allow detecting potential malfunctions in the circuit. Another common use of waveguide couplers is to allow injecting an additional signal into a waveguide network.
An example of a typical cross-guide waveguide coupler 200 is shown at FIG. 1. As shown, the waveguide coupler 200 comprises a main waveguide arm 202 and a secondary waveguide arm 204 transversely positioned relative to the main arm 202 and fastened thereto in a suitable manner (e.g., via welding). Each of the main arm 202 and the secondary arm 204 consists of a hollow metallic conduit within which RF energy propagates. The main arm 202 comprises first and second waveguide ports 206, 208 while the secondary arm 204 comprises third and fourth waveguide ports 210, 212. For the purpose of this example, the first port 206 is an “input port” and the second port 208 is an “output port” or a “transmitted port” such that RF energy inputted at the first port 206 propagates through the main arm 202 towards the second port 208. In order to couple RF energy from the main arm 202 to the secondary arm 204, a coupling element comprised of one or more apertures (not shown) is provided in the adjacent walls of the main arm 202 and secondary arm 204. In a specific practical example, the apertures may allow a portion of the RF energy propagating through the main arm 202 from the first port 206 the second port 208 to be diverted and transmitted to the third port 210 which may be referred to as a “coupled port”. In such example, the fourth port 212 of the secondary arm 204 is typically used as an “isolated port” and is terminated by coupling it to a matched load (not shown). The third port 210 is typically connected to a detection circuit (not shown) configured to measure/monitor the RF energy released at the third port 210. The transmission of the RF energy within the coupler 200 is conceptually illustrated in FIG. 2.
FIG. 3 illustrates an example of a coupling element including an aperture 214 that may be used to couple RF energy from the main arm 202 to the secondary arm 204. In this specific example, the aperture 214 is cross-shaped such that it comprises a generally vertical slot and a generally horizontal slot positioned so that the two slots intersect one another substantially at the mid-point of each slot. On the main waveguide arm 202, the aperture 214 is positioned such that its horizontal slot is generally transversal to a longitudinal extent of the main 202 while the vertical slot is generally aligned with the longitudinal extent of the main arm 202. The shape and dimensions of the aperture 214 affect the coupling of the RF signal from the main arm 202 to the secondary arm 204. For additional informal pertaining to typical cross-guide waveguide couplers of the type described, the reader is invited to refer to J. A. R. Ball and T. M. Sulda, “Crossed Waveguide Directional Couplers for High Power Applications”, J. Microw. Power Electromagnetic Energy, vol. 35, no. 4, pp. 232-241, the contents of which are incorporated herein by reference.
FIGS. 4A to 4D illustrate a RF magnetic field of the RF wave near the cross-shaped aperture 214 at times t=0, t=T/4, t=T/2 and t=3T/4 respectively, where T is the time for one guided wavelength period. As shown, at t=0, the magnetic field is oriented downwards (i.e., in a direction transversal to a longitudinal extent of the main arm 202) such that the coupling to the secondary arm 204 of the coupler 200 is mostly done via the vertical slot of the cross-shaped aperture 214. At t=T/4, the magnetic field is oriented horizontally (i.e., in a direction parallel to the longitudinal extent of the main arm 202) such that the coupling to the secondary arm 204 of the coupler 200 is mostly done via the horizontal slot of the cross-shaped aperture 214. It will be appreciated that the magnetic field in FIGS. 4A to 4D rotates in a counter-clockwise direction. This rotation of the magnetic field is the same in the secondary arm 204 of the coupler 200 and determines the transmission direction of the RF signal within the secondary arm 204. The magnetic field therefore plays a significant role in the quality of the coupling between the main arm 202 and the secondary arm 204.
Traditional waveguide couplers of the type depicted in FIG. 1 tend to be bulky in view of the relatively large cross-section of each of the main arm 202 and the secondary arm 204, which for some practical applications may be undesirable.
In light of the above, there is a need in the industry for an improved cross-guide coupler that alleviates, at least in part, the deficiencies with existing couplers.